According to media reports, top cyclists use ketones. Thanks to these new sports supplements, athletes could burn more fat and perform at a higher level, countless journalists report. No wonder that interest in ketones is also growing in fitness and bodybuilding. But before you buy ketones, it is good if you understand that ketone supplements come in shapes and sizes.

Ketones
Ketones are pieces of fat molecules that are released when the body converts fats into energy. When people fast, or if they significantly reduce the amount of carbohydrates in their diet, the amount of ketones in their blood increases dramatically. That is why a strict low-carbohydrate diet is called 'keto diet'.

The two most important ketones are beta-hydroxy butyric acid (BHB) and acetoacetate.

There are small studies in which, for example, elite soldiers perform better due to a diet with particularly low carbohydrates, but in a number of larger studies there is often little left of those interesting effects. [J Spec Oper Med. Summer 2017;17(2):112-6.] But we're not going to talk about low-carb diets.

Effects of ketones
Ketones probably play an important role in the positive effects of fasting or a low-carbohydrate diet, such as cells that become more sensitive to insulin, muscles that absorb nutrients from the blood more easily and tissues that invest more energy in recovery processes. In a way that scientists do not yet fully understand, ketones stimulate those processes.

Ketones also have remarkable psychological effects. Once the body is accustomed to using fat as the main fuel - it can take a few weeks when switching to a low-carbohydrate diet, with fasting a few days - people become more energetic, hungry, clearer and often even euphoric. This is probably because ketones are an excellent source of energy for the brain.

So it is not so strange that in the first half of the 1980s nutritional scientists came up with the idea of ​​giving ketones as a supplement to athletes. Those athletes don't fast and continue to eat carbohydrates, but thanks to the ketone supplements can still benefit from the positive effects of a low-carb diet or a diet of fasting.

At least, that's the idea.

Ketone salts
Anyone looking for ketone supplements in web stores will mainly find ketone salts. These are mixtures of compounds between BHB and minerals such as sodium, magnesium and potassium. According to the supplement industry, athletes who use 30-50 grams of ketone salts daily can perform at a high level for longer and burn more fat.

These side effects may be due to the hefty amount of minerals that athletes ingest when they use ketone salts. It is so high that long-term use of ketone salts without intensive medical supervision is dangerous.

Another possible reason for the disappointing results of ketone salts supplementation is that ketone salts do not contain one type of BHB, but a mixture of two types of BHB molecules: D-BHB and L-BHB. Chemists call such a mixture 'racemic'.

Physiologists suspect that racemic mixtures of BHB do not have a performance-enhancing effect. In the human body you mainly find D-BHB, and only a few L-BHB. The body converts D-BHB into energy, but not L-BHB. Supplementation with D-BHB has positive effects, supplementation with L-BHB has no effect or even a negative effect.

1,3-Butanediol-Acetoacetate-Di-Ester
Yet another potential ketone supplement is 1,3-butanediol-acetoacetate diester [bottom right]. This too is a racemic mixture of compounds that convert in the body into D and L variants of 1,3-butanediol and acetoacetate. If you give cyclists 1,3-butanediol-acetoacetate diester, their performance will deteriorate. [Front Physiol. 2017 Oct 23;8:806.]

D-BHB-Mono-Ester

If you synthesize organic compounds in bioreactors, you quickly make racemic mixtures. This also applies to the ketone supplements that we have already discussed and that are probably not working for this reason. However, it does not apply to D-BHB monoester [top left].

The media reports on the use of ketones in elite sport relate to this specific ketone supplement.

Not surprisingly, ketone supplementation increases endurance capacity by a few percent. This sounds modest, but in cycling, the effect of these few percent is immense.

There is hardly any research into the use of D-BHB mono-ester in strength sports, but it seems that ketones can accelerate recovery after strength training. [Front Physiol. 2017 May 23;8:310.]

It all sounds great, but you have to remember that practically all the studies that we now have have been fully or partially carried out by its inventors. Those inventors have patented D-BHB mono-ester, and set up companies [hvmn.com] that sell the ketone supplement.

If as many athletes use ketones as the sports media suggest, those companies will make a profit. An average athlete who uses D-BHB mono-ester needs just over 50 euros a day.